174 



RELICS OF PRIMEVAL LIFE 



microscopically, however, they differ very much 

 among themselves, and it may be that some of 

 them were Hydroids and some Protozoa. The oldest 

 that we at present know, and consequently the near- 

 est in time to Eozoon, impress us rather with the 

 latter affinity. They are the fossils of the genus 

 Cryptozoon of Hall (Fig. 7^), which form great 

 masses filling certain beds of Upper Cambrian age, 



Vv;vi'vv*^-< 



| -J/^/,^ 



Fig. 45. — Tubular Strutuite of Ccenostroma, Silurian. 



and which, when sliced and studied microscopically, 

 are found to consist of concentric thin laminae filled 

 in between with a porous mass of calcareous matter 

 penetrated by an infinity of. tortuous tubes. Forms 

 of this kind have been traced downward into pre- 

 Cambrian beds in Colorado, and as we shall find in 

 New Brunswick, into the Upper Laurentian itself. 

 They present, however, structural differences from 



^ See Figs. 7 and 8, pp. yj^ 39 ; also Fig. 8 and Microscopic 

 slice, Fig. 61, at end. 



